The role of the RNA regulon in the control of gene expression

Protein synthesis is the process by which the information in the genetic material in the cell, DNA, is converted via an intermediary substrate mRNA, into proteins. For proteins to be synthesised the mRNA must interact with a large complex called the ribosome which consists of RNAs and proteins. Ribosomes are able to decode the genetic information that is held in the mRNA and carry out the synthesis of the proteins. When mammalian cells are exposed to external agents that can damage the cell one of first things to happen is that protein synthesis is almost totally switched off. This is part of the cell's defensive mechanism since it allows the cell to repair the damage and recover from stress. However, whilst overall protein synthesis is decreased under these types of conditions, certain proteins still need to be made that allow the cell to recover from the damage. For example, we have shown that following treatment of cells with the type of UV-light that is found in sunlight, there is increased synthesis of proteins that are required to repair the damage that is caused to the DNA by this light. We have also found that under these conditions the cells use a different mechanism to synthesise proteins. However, data from other researchers have shown that under different conditions of cell stress e.g. when there is a reduced amount of oxygen present, different subsets of proteins are synthesised that are specific to the type of stress induced. This shows that there is coordinated regulation of protein synthesis following cell insult. The important question that needs to be addressed is how does this occur? Our results suggest that the mRNAs that are translated during cell stress contain important information in their non-coding regions (untranslated region UTR) that allows their recruitment to the ribosomes. In this proposal we aim analyse large amounts of data to identify the regions within the mRNAs that allow ribosome recruitment under different conditions of cell stress.

Under conditions of patho-physiological cell stress post transcriptional regulation of gene expression is achieved by the reprogramming protein synthesis. For example, following exposure of cells to UV-light, hypoxic conditions and ER stress there is a general shut-down of protein synthesis which is mediated, in the most part, by a reduction in the levels of ternary complex. Under each of these situations there is selective recruitment to the ribosomes of mRNAs whose protein products are required as part of the response to the stress. For example, our data have shown that following exposure of cells to UV-light there is a selective increase in the polysomal association and corresponding synthesis of DNA repair enzymes. The key question that now needs to be addressed, that is fundamental to our understanding of post-transcriptional control of gene expression, is how selectivity is achieved. Two broad approaches will be used to answer this question. A detailed analysis of the components that comprise the post-transcriptional DNA damage response will be carried out by performing a range profiling studies to determine the mRNAs that remain polysomally associated following DNA damage, to identify and examine the RNA regulatory elements within their 5' and 3' UTRs, and determine the roles of key proteins in this response. An International Centre of Expertise will be established at Nottingham that will both coordinate post-transcriptional profiling data (generated in Nottingham and elsewhere) and provide access to others in the UK who are carrying out research in this area, but do not have access to the technology and/or expertise required. The data from these additional studies will also be subject to bioinformatics analysis and thus we will be in a unique position to extract the maximum amount of information from the data generated from these types of experiments, and to curate this information for the benefit of the UK (and world-wide) research community.